The long term goal of this research is to understand how sensory cues from the semicircular canals (measuring rotation) and the visual system (measuring orientation and motion) influence the interpretation of sensory cues from the otolith organs (measuring gravity and linear acceleration). To accomplish this goal, this proposal focuses on the study of adaptive changes in the interpretation of otolith cues caused by transitions to altered gravitational environments. Understanding these key systems-level processes underlying vestibular compensation and dynamic adaptation will provide the foundation to facilitate the development of targeted behavioral approaches for the management of balance and vestibular disorders and adaptation to altered gravitational environments. The seven specific aims of this grant are: 1. Investigate how the human nervous system resolves otolith measurements of gravito-inertial force into estimates of gravity and linear acceleration in a 1-G environment. 2. Investigate how the nervous system resolves gravito-inertial force into estimates of gravity and linear acceleration in hypergravic environments. 3. Investigate adaptive changes in how the human nervous system resolves otolith measurement of gravito-inertial force into estimates of gravity and linear acceleration in hypergravic environments. 4. Investigate to what extent responses to high frequency inertial stimuli, normally interpreted primarily as translation, can be adapted to yield increased tilt responses. 5. Investigate to what extent responses to low frequency inertial stimuli, normally interpreted primarily as tilt, can be adapted to yield increased translation responses. 6. Investigate to what extent context specific adaptation of graviceptor mediated tilt and translation occurs. 7. Develop and test our systems approach model of visual-vestibular interactions. The experimental specific aims will be addressed by measuring eye movements and perceptual responses. The modeling specific aim will be addressed using numerical computer simulations.